Transistorized control circuit for magneto motor ignition systems

ABSTRACT

During the negative half cycle of the magneto output voltage, a capacitor in series with a diode is charged to a voltage limited by a Zener diode of a negative limiting circuit. During the next positive half cycle the sum of the magneto voltage and the capacitor voltage are applied over a current limiting resistor to the base of a power transistor in the primary circuit, holding the latter turned on until a timing pulse applied to a control transistor short circuits the base-emitter path of the power transistor, switching off the latter and permitting the capacitor to discharge. The interruption of the primary current produces a spark in the secondary circuit, the armature of the magneto being wound to serve also as an ignition coil.

United States Patent [191 Haubner et a1.

[4 1 Feb. 4, 1975 TRANSISTORIZED CONTROL CIRCUIT FOR MAGNETO MOTOR IGNITION SYSTEMS [75] Inventors: George Haubner, Berg; Walter Hofer, Schwabach; Peter Schmaldienst, Nurnberg, all of Germany [73] Assignee: Robert Bosch Gmbll, Stuttgart,

Germany 221 Filed: July 31,1973

21 Appl. No.: 384,381

[30] Foreign Application Priority Data Aug. 29, 1972 Germany 2242327 [52] US. Cl 322/17, 123/148 E, 310/70 A,

315/209 T, 315/218 [51] Int. Cl. F02p 1/00, F02p l/08, F02p 9/00 [58] Field of Search 310/70 R, 70 A; 322/17, 322/91, 94; 315/218, 209 R; 123/148 E, 148 MCD [56] References Cited UNITED STATES PATENTS Piteo 310/70 R 3,496,920 2/1970 Shano et a1. 310/70 R 3,504,373 3/1970 Strelow 315/218 3,750,637 8/1973 Minks 123/148 MCD Primary Examiner.l. D. Miller Assistant Examiner-Robert J. Hickey Attorney, Agent, or Firm-Flynn & Frishauf [57] ABSTRACT During the negative half cycle of the magneto output voltage, a capacitor in series with a diode is charged to a voltage limited by a Zener diode of a negative limiting circuit. During the next positive half cycle the sum of the magneto voltage and the capacitor voltage are.

applied over a current limiting resistor to the base of a power transistor in the primary circuit, holding the latter turned on until a timing pulse applied to a control transistor short circuits thebase-emitter path of the power transistor, switching off the latter and permitting the capacitor to discharge. The interruption of the primary current produces a spark in the secondary circuit, the armature of the magneto being wound to serve also as an ignition coil.

9 Claims, 2 Drawing Figures TRANSISTORIZED CONTROL CIRCUIT FOR MAGNETO MOTOR IGNITION SYSTEMS Cross reference is made to the following applications of the same inventors:

Ser. No. 384,282, filed July 31. l973 Ser. No. 384,380, filed July 3l, I973.

This invention concerns an ignition control circuit for a magneto ignition system of an internal combustion engine. In particular it relates to ignition systems using a controllable semiconductor device such as a transistor with its switching path in the primary current circuit of an ignition coil, the secondary winding of which is connected by an ignition cable with. at least one spark plug. The invention further relates to transistorized magneto ignition circuits in which thesemiconductor device has its control electrode connected to a control circuit in which a control signal at the proper ignition time switches the semiconductordevice from conducting to nonconducting condition.

In so-called coil ignition systems a previously closed primary current circuit is opened at the time for ignition by the semiconductor device, which is preferably a power transistor. When that happens the magnetic field built up in the ignition coil collapsesand induces a high voltage pulse in the secondary winding, which sets off a spark in the spark plug.

Thereafter, the primary circuit must be closed anew to make possible the generationof further sparks. In battery-powered ignition systems the necessary voltage for switching the ignition transistor back to its conducting state can be taken from the battery. In the so-called magneto ignition systems, however, the voltage at the output terminals of the magneto generator armature is too small, when the primary circuit is short circuited, to hold the ignition transistor fully in its conducting condition. For the building up of astrong magnetic field in the ignition coil or in the magneto'armature (when that is provided with a secondary, so that it can function as an ignition coil also), it is necessary to keep the ignition transistor fully conducting.

In a known form of transistorized magneto ignition systems, the ignition transistor is connected in series with a resistor in the primary circuit. When a positive half wave of the magneto armature is applied to the circuit, the voltage drop across this resistor switches the ignition transistor into its conducting condition and maintains it thus until the time for ignition. At the time of ignition the base-emitter path of the ignition transistor is short circuited, in consequence of which the ignition transistor is blocked. This and similar solutions of the problems have the disadvantage that the resistor loads down the primary circuit in an undesired way, because it has the effect of limiting the current and thus allowing only a limited build-up of the magnetic field in the magneto armature during the positive half waves. When the primary circuit is interrupted by the transistor, therefore, the high voltage then produced in the secondary winding of the armature is greatly reduced.

It is an object of the invention to provide a transistorized magneto ignition system in such a way thatthe magnitude of the primary current to be interrupted at the ignition time is substantially uneffected by the presence in the primary circuit of control elements for the ignition transistor.

Subject matter of the present invention:

Briefly, across the armature winding, or the primary winding if there are two windings on the armature to provide an ignition coil function, there is bridged a series, circuit containing a capacitor and a diode, the diode being connected with polarity opposite to that of the switching path of the semiconductor device in the primary circuit, and the common connection of the capacitor and the diode is connected to the control electrode of the semiconductor device. In order to protect the latter, the connection between its control electrode and the junction of the capacitor and the diode is made by a resistor. The semiconductor device in the primary circuit is preferably a power transistor.

Since in the circuit just described the negative half waves of the magneto output charge the capacitor and the latter puts and holds the ignition transistor in its conducting condition during the succeeding positive voltage half wave, the primary current circuit is therefore directly short circuited by the ignition transistor and a strong primary current can flow and there is no need to insert any resistors in the primary circuit to provide the control voltage for the transistor. The build-up of current is therefore not limited appreciably by control circuitcomponents.

The invention will be described by way of example with reference to the accompanying drawing, wherein:

FIG. I is a circuit diagram of a transistorized magneto ignition system according to the invention, and

FIG. 2 is a timing diagram showing the course of currents and voltages in the control circuit of the transistor and in the primary circuit of the ignition system shown in FIG. 1.

FIG. I shows an ignition system for a one-cylinder gasoline engine provided with a magneto generator 10 the armature ll of which is provided with a two-part winding 12, which at the same time provides the ignition coil of the ignition system. The stationary armature 11, mounted on the casing of the gasoline engine, operates with a rotating magnetized rotor 13, provided with a permanent magnet 13a. This rotor is driven by the engine. The secondary winding 12a of the magneto armature 11 is connected by an ignition cable 14 with a spark plug 15; The primary winding 12b of the armature I1 is connected in a primary current circuit in which the collector-emitter path of an ignition transistor 16 also lies. The transistor 16 is an NPN power transistor, and its emitter connection is grounded to the vehicle chassis or the engine casing, as is also one end of the primary winding 12h. That winding is bridged by a series combination of a capacitor I7 and a diode I8, the polarization of which is opposite to that of the collector-emitter path of the ignition transistor 16. The common connection 19 of the capacitor 17 and the diode I8 is connected to a resistor 20, the other end of which is connected to the base of the ignition transistor 16, where a further control circuit is also connected comprising a control transistor 21 arranged with its collector-emitter path parallel to the base-emitter path of the ignition transistor 16.

A magnetic pulse generator 22 provides the timing of the spark, and for that purpose its output is connected across the base-emitter path of the control transistor 21. The base of the control transistor 21 is, furthermore, connected over a resistor 23 with the grounded end of the primary winding 12b and also connected over a coupling resistor 24 with the other (ungrounded) end of the primary winding 12b. The primary winding 12b is. furthermore bridged by a negative peak reducing device 25 that operates during negative voltage half waves in the primary circuit. The negative peak reducing device 25 contains a diode 26 in series with a Zener diode 27. The diode 26 is poled opposite to the polarity of the collector-emitter path -of the ignition transistor 16. The Zener diode 27 is so poled that when the Zener voltage is reached, current will pass over the diode 26 and the Zener diode 27 and cause the negative peak voltage in the primary circuit to be limited. To relieve the ignition transistor 16 during negativevoltage half waves, a second diode 28 is interposed in the primary circuit, poled for conduction on positive voltage half waves.

The operation of the ignition system of FIG. 1 is best understood with reference to the timing diagram of FIG. 2, in which current and voltage curves are shown.

Relative to the axis an; are shown the course of the primary voltage U,,, by a dashed line, and that of the primary current l,,, by a solid line. Relative to the axis w are shown the base voltage U,, of the transistor 16, by a dashed line, and the base current l,, of the transistor 16, as a solid line, as well as the charge voltage U of the capacitor 17, by a dotted line.

When the gasoline engine is running, the permanent magnet 13a of the magnetic rotor 13 is rotated so as to move past the stationary armature ll of the magneto, producing an alternation of negative and positive voltage half waves. When a negative voltage half wave is induced in the primary winding 12b of the armature 11, the output voltage is limited to the Zener voltage of the Zener diode 27, for when the latter conducts it provides a conducting bridge over the diode 26 across the primary winding terminals. The capacitor 17 is accordingly charged over the diode 18 to the voltage of the negative half wave as limited by the Zener diode 27. The diode 18 conducts while the capacitor 17 charges, so that the voltage provided to the base ofthe transistor is essentially the reference chassis voltage. When the negative half wave voltage drops below the Zener voltage, the diode 18 stops conducting and the voltage of the junction 19 goes positive, continuing to go more positive as the end of the negative half wave gives way to the succeeding positive half wave. The voltage of the junction 19 is communicated to the base of the transistor 16 over the resistor 20. Consequently, at the end of the negative voltage half wave the capacitor voltage U, becomes effective as the base voltage U between the base and the emitter of the ignition transistor 16. As the positive half wave of the primary winding 12b of the armature comes on, the positive voltage is superimposed on the capacitor voltage U so that the base voltage U is further increased. This base voltage U,, gives rise to a base current I which puts the ignition transistor 16 fully in its conducting condition, so that the primary circuit of the magneto is practically short circuited The primary current l rises to a peak value and builds up astrong magnetic field in the armature 11. The base voltage U, does not rise much because of the voltage drop in the resistor 20 resulting from the base current.

At the time for ignition a voltage pulse is produced by the magnetic pulse generator 22, which raises the base of the control transistor 21 to a positive potential and thereby switches the control transistor 21 to its conducting condition. The base-emitter path of the ignition transistor 16 is thus short circuited, and the base voltage U, according, collapses. lnconsequence, the base current l,, is switched off, and at the same time the capacitor 17 discharges over the resistor 20 and the collector-emitter path of the control transistor 21. The ignition transistor 16 is immediately blocked by the switching off of the base current l,,. as the result of which the primary current l,, is interrupted. The magnetic field in the armature 12 now collapses and thereby induces a high voltage pulse in the secondary winding 12a, which sets offa spark in the spark plug 15.

Since the collapse of the magnetic field in the armature also induces a voltage in the primary winding 12b, it must be assured that the control transistor 21 is held in its conducting condition. The coupling resistor 24 provides this assurance, as well as an accelerated switching over of the control transistor 21. The coupling resistor 24 transmits the rise of the primary voltage to the base of the control transistor 21, and thereby holds that transistor in its conducting condition even if the control pulse provided by the pulse transmitter 22 has already dropped off. Only at the end of the positive half wave of the primary voltage U, does the control transistor 21 regain its nonconducting condition by virtue of the connection of the resistor 23 between base and emitter. During the succeeding negative half wave in the primary winding 12b, the capacitor 17 can be recharged. The ignition cycle and the charging up of the capacitor 17 repeats with each full revolution of the magnetic rotor 13.

Although the invention has been described with respect to a particular illustrative embodiment, it is not limited thereto but also includes circuits in which particular components are differently constituted. What is important is that when the positive voltage half wave arises in the primary circuit, the semiconductor device inthe primary circuit must be switched fully on during the entire portion of the cycle to the time of ignition, because the control voltage for the semiconductor device is so greatly increased by the series addition of the primary voltage and the voltage of the previously charged capacitor that even at low speeds of the engine, and hence of the magneto rotor 10, a sufficient switching on of the semiconductor device is obtained. The semiconductor device 16, instead of being an individual power transistor as shown in FIG. 1, could likewise be a pair of transistors in the well-known Darlington circuit. Likewise, the control transistor 21 could be replaced by a semiconductor controlled rectifier (SCR, sometimes called a thyristor), an SCR tetrode or a triac, in which case the coupling provided by the voltage divider constituted by the resistors 24 and 23 could be dispensed with. It is also possible to provide bridging of less than the entire primary winding 12b of the armature 11 by the capacitor 17 and the diode 18, or likewise by the negative peak limiting circuits 25. A further change of the circuit of FIG. 1 within the concept of the present invention is to use an ignition coil separate from the armature 11 arranged at another point in the primary circuit. Such a separate ignition coil is an equivalent of double-winding of the armature with a low-voltage and a high-voltage winding, the purpose in each case being to derive a high voltage from the interruption .of a heavy current in a low-resistance circuit operating at low voltage by the well-known transformer step-up effet. In any case, the switching path of the first semiconductor device 16 is interposed in the primary circuit so that when it is in its conducting condition a heavy current flows through said primary circuit as the result of the voltage induced in the low voltage armature winding, and when the switching path of the first semiconductor device 16 is suddenly put into its nonconducting condition, the current in the primary circuit, and hence in the low voltage coil of the spark coil, is interrupted and the collapse of the magnetic field of the spark coil, whether the spark coil be built into the magneto generator or separate, induces a high voltage in the high voltage winding. In either case, the high voltage winding is herein regarded as a voltage step-up means coupled with the magneto armature.

It is finally also possible to provide for charging the capacitor 17 from a source external to the primary circuit.

We claim:

1. In an internal combustion engine ignition system having a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine, and having voltage step-up means coupled with said magneto armature, which means is coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug, said ignition system having also a spark-timing pulse generator operated in synchronism with said 'engine,

an ignition control circuit for connection to said lowvoltage winding of said armature, comprising:

a controllable semiconductor device (16) having a switching path and a control path and having its switching path in circuit with said low-voltage winding and its control path in a control circuit;

means (21) to supply the spark-timing pulse output of said pulse generator (22) to the control circuit of said semiconductor device (16) in such polarity as to put the switching path of said semiconductor device quickly into its non-conducting condition and thereby interrupt the current in said lowvoltage winding;

a series combination of a capacitor (17) and a diode (18) connected so as to bridge at least a substantial part of said low-voltage winding (12b), said diode being poled for conduction in the direction opposite to the direction of conduction of said switching path of said semiconductor device (16), and

a resistively conductive connection between said ,which the resistively conductive connection between said common connection (19) of said capacitor (17) and said diode (l8) and said control electrode of said semiconductor device (16) includes a resistor (20) through which said connection is effected.

3. An ignition control circuit as defined in claim 2 in which a second controlled semiconductor device (21) is provided in the control circuit of said first semiconductor device (16), with its switching path connected in parallel to the control path of said first semiconductor device (16).

4. An ignition control circuit as defined in claim 3 in which said first controlled semiconductor device is a transistor, having a collector-emitter switching path and a base-emitter control path.

5. An ignition control circuit as defined in claim 4 in which said second controlled semiconductor device (21) is also a transistor.

6. An ignition control circuit as defined in claim 3 in which said pulse generator (22) is a magnetic pulse generator driven by said engine.

7. An ignition control circuit as defined in claim 6 in which a coupling resistor (24) is provided between an ungrounded terminal of said low-voltage winding (12b) of said armature and the control electrode of said second semiconductor device (21).

8. An ignition circuit as defined in claim 6 in which said low-voltage winding (12b) is bridged by unidirectional peak-reducing means providing a current path.

(25), including a diode (26) poled for conduction in the direction opposite to the direction of conduction of said switching path of said first semiconductor device (16).

9. An ignition circuit as defined in claim 8 in which said diode (26) of said peak-reducing means (25) is connected in series with a Zener diode (27). 

1. In an internal combustion engine ignition system having a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine, and having voltage step-up means coupled with said magneto armature, which means is coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug, said ignition system having also a spark-timing pulse generator operated in synchronism with said engine, an ignition control circuit for connection to said low-voltage winding of said armature, comprising: a controllable semiconductor device (16) having a switching path and a control path and having its switching path in circuit with said low-voltage winding and its control path in a control circuit; means (21) to supply the spark-timing pulse output of said pulse generator (22) to the control circuit of said semiconductor device (16) in such polarity as to put the switching path of said semiconductor device quickly into its non-conducting condition and thereby interrupt the current in said low-voltage winding; a series combination of a capacitor (17) and a diode (18) connected so as to bridge at least a substantial part of said low-voltage winding (12b), said diode being poled for conduction in the direction opposite to the direction of conduction of said switching path of said semiconductor device (16), and a resistively conductive connection between said control electrode of said semiconductor device (16) and the common connection (19) of said capacitor (17) and said diode (18).
 2. An ignition control circuit as defined in claim 1 in which said series combination of a capacitor and a diode bridges all of said low-voltage winding and in which the resistively conductive connection between said common connection (19) of said capacitor (17) and said diode (18) and said control electrode of said semiconductor device (16) includes a resistor (20) through which said connection is effected.
 3. An ignition control circuit as defined in claim 2 in which a second controlled semiconductor device (21) is provided in the control circuit of said first semiconductor device (16), with its switching path connected in parallel to the control path of said first semiconductor device (16).
 4. An ignition control circuit as defined in claim 3 in which said first controlled semiconductor device is a transistor, having a collector-emitter switching path and a base-emitter control path.
 5. An ignition control circuit as defined in claim 4 in which said second controlled semiconductor device (21) is also a transistor.
 6. An ignition control circuit as defined in claim 3 in which said pulse generator (22) is a magnetic pulse generator driven by said engine.
 7. An ignition control circuit as defined in claim 6 in which a coupling resistor (24) is provided between an ungrounded terminal of said low-voltage winding (12b) of said armature and the control electrode of said second semiconductor device (21).
 8. An ignition circuit as defined in claim 6 in which said low-voltage winding (12b) is bridged by unidirectional peak-reducing means providing a current path (25), including a diode (26) poled for conduction in the direction opposite to the direction of conduction of said switching path of said first semiconductor device (16).
 9. An ignition circuit as defined in claim 8 in which said diode (26) of said peak-reducing means (25) is connected in series with a Zener diode (27). 